You don't need to be a chef to criticize the meal. Otherwise all the people reviewing multimeters here would be guilty of the same issue, right? And Dave too--how many scopes has he designed?
You don't need to be a chef but unless you are actually a chef you are unlikely to understand (or even be aware of) a lot of the rationale that went into the design. Anyone can criticize, but the weight such criticism carries tends to be proportional to their experience ...
Furthermore, if you look at costs of COTS components, the fancy button panel and TFT LCD that John Kenny designed probably a) wasted a bunch of his valuable time b) cost more than taking a commodity capacitive tablet display and a few pots coupled with a common graphical UI c) can't be reused on any other tool without serious rework. All this means that despite him getting it designed down to cost, it's ultimately a one-off. Even he admits that Keysight has historically been quite bad at reuse.
I keep coming back to the r&s rtb2000 series because it clearly looks like R&S realized this and have developed a common chassis with touchscreen and a few multifunction knobs and buttons and can swap out the hardware to e.g. make that new spectrum analyzer. They can then use this commonality to drive a better graphical UI, and can put the economies of scale from having 1 display and 1 set of physical controls to use in paying for better components. Unfortunately they decided to piss on people in the UK and didn't offer their launch deal here otherwise I'd have been on it.
And, if they did it right, when the market demands 3d VR scopeview nextgen 5000+++ they can just swap out the display hardware rather than having it tightly coupled to their measurement engine, like with MegaZoom IV (seriously whoever decided that ought to be slapped, what a dumb move)
So you are comparing a custom panel with a COTS tablet. I guess you have totally missed the part when that product has been designed (5+ years ago) - how many cheap COTS tablets with capacitive touch have been available back then? First iPad that has introduced this technology to the mass market showed up in 2010, some 7 years ago. And requiring a high powered SoC to drive it thanks to the high speed interface. Not a problem on the iPad where you need it anyway but would you accept $200 extra cost on a multimeter or a power supply for this?
Also how long does a tablet screen typically remain on the market? 6-12 months? What will you do afterwards? Ditch your R&D and redo the product from scratch because the display isn't available anymore? E.g. their the HP 34401A bench meter stopped being officially supported only last year - after 24 years. And the replacement parts (e.g. to fix the dim VFD displays) are still available for it.
At our company we have been facing exactly this decision for a simulator screen. After realizing that we will certainly not be able to replace or update a tablet used for the screen once it breaks because it will not be available anymore, we have gone with much less fancy but more robust solution using an industrial touch screen that will be available even 10 years later.
This is why you won't see these tablet displays in products that are meant for industrial (as opposed to consumer) markets.
The R&S RTB2000 is a much newer product than the Keysights you are criticizing (which are on the market for years now and took another several before to develop). When the MegaZoom IV was developed it was pretty much the only way of doing things, considering the amount of high speed data you need to transfer. And again, hindsight is wonderful but one cannot design products with components that will only become available almost a decade later!
John Kenny even admits that NI does exactly this: they designed one really really really good voltmeter (I think) and then turn all their other measurement tools into frontends for that. They then spent time on making a decent (for t&m) software, labview (yes, i know) that they can sell for a much, much higher margin than any hardware.
He also said that Keysight is doing this (or going in that direction) too. Why do you think he spoke about unifying the front panels and transferring the know-how across the various departments? It is literally his job to ensure it.